In the waterproof application of a rooftop, a veranda, a corridor, or the like of an architectural construction, or the covering application of a structure in which an impact buffering function is required (such as a play equipment or the like), two-agent mixture-cure type resin or moisture-cure type resin, such as polyurethane, is widely used.
At the time of the application, with a spray gun, raw material liquid is sprayed on an application object, thereby forming a resin layer.
For the resin layer, a function (a substrate treatment function) to adjust to concavity/convexity, unevenness, a difference in level, gaps or the like of a substrate of the application object, is required. Also, it is preferable to have a high buffering function against behavior (movement) such as expansion, contraction, or deformation of the substrate. Further, in order to achieve a longer service life of a structure, reducing weight is also required for a resin layer which is formed on the structure.
In recent years, to deal with these demands, using a low-density resin layer which is made of fast-cure type urethane resin has been studied.
In order to form the low-density resin layer, for example, by using a spray gun having a structure in which gas is introduced, spray application is performed while gas is supplied into a nozzle section of the spray gun.
In the spray gun, in order to prevent the inflow (backflow) of a raw material liquid to a gas introduction path, transport pressure of the raw material liquid is set to be relatively low and supply pressure of the gas is set to be relatively high.
Since transport pressure of the raw material liquid is low and mixing is prone to be insufficient, a spray gun with a built-in agitation device which agitates the raw material liquid is proposed (refer to PTL 1, for example).